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Re: Compressor Pump Down

Yes. Close the liquid outlet valve of the receiver and let the compressor run. Details:

Have your gauges connected to both the low and high side of the compressor.

Watch the high side to insure that the receiver does not fill up with liquid and cause your discharge pressure to rise above a reasonable level because it is rising into the condenser.
Relieve the high side pressure into the suction and do another pump down cycle. If all is well, you have a small amount of vapor to recover with your recovery unit.

I am sure there are other techniques used by others. I will read their responses to see if there are better ways.

Re: Compressor Pump Down

Originally Posted by KETTLER

Thanks Dan,

Do I pull a 500 micron vacuum on the compressor head and then charge it with some refrigerant after I install the new pressure switches?

Thanks,
KETTLER

Where is the hp / lp switch fed from.
You need to be careful because if they are fed from the service valves then it is important to know how the valve is seated.
If the switches are fed straight from the comp body then just isolate the comp, valve off the comp from the pipework and then remove the gas from the comp. Change the switches and pressure test. Then vac the body of the comp. Open system up and run on test.

Re: Compressor Pump Down

Will I be able to save refrigerant if I pump it into the LIQUID RECEIVER before I isolate and open the compressor?

Can the compressor pump all the refrigerant into the LIQUID RECEIVER and CONDENSER without undergoing a high pressure failure?

KETTLER

I would just shut the suction valve while the comp is running. Then when the comp shuts down shut the discharge valve. The amount of gas in the comp will be minimal. To get the pressure even lower short out the lp switch and let the comp run into a vac. When all valves are closed vent the discharge gas from the comp head back to the suction and that will reduce further any gas loses.
Change the switches and then test like normal.

Re: Compressor Pump Down

Thanks All!

So, my proceedure seems to be as follows:

1. Close (frontseat) the SERVICE VALVE on the LIQUID RECEIVER.
2. Close (frontseat) the SUCTION SERVICE VALVE.
3. Bypass the LOW PRESSURE SWITCH.
4. Run the compressor until a vacuum is achieved.
5. Close the DISCHARGE SERVICE VALVE on the compressor.
6. Remove the existing pressure switch probes and replace them with the new switch probes.
7. Evacuate the COMPRESSOR HEAD.
8. Charge the COMPRESSOR HEAD with a shot of refrigerant (vapor).
9. Open the SERVICE VALVES and run the system.

I still don't understand how the compressor can run with the SERVICE VALVE closed on the LIQUID RECEIVER and not cause internal damage? Does the compressor discharge pressure drop off once all the refrigerant is condensed and moved to the LIQUID RECEIVER?

Re: Compressor Pump Down

g day kettler
try this, put your gauges on the comp high and low sides... now front seat the suction service valve an let the comp cut out on the LP control.....if it stops above 0 psig short out the LP control and let the comp run till you get to 0 psig [a tiny bit higher is good no crap gets sucked in the system] now turn the comp off....front seat the discharge service valve....bleed the pressure from the high side to the low side....you should now have bugger all pressure in the comp....change the HPLP control... when you have done that close your gauges an crack the suction valve.....purge a puff or two from the high side gauge line to be sure thre is no air left in the comp head....now open both service valves an kick the bugger in the guts...test the operation of the new control an fine tune if needed...dont touch your liquid line service valve... you only need to isolate the comp...now thats done grab a ice beer from the esky.....good luck mate

Re: Compressor Pump Down

How will my LP gauge read the pressure in the compressor head if I close the SUCTION SERVICE VALVE?

It wont. It will read crankcase pressure.

1. ignore any liquid valves.

2. Close (frontseat) the SUCTION SERVICE VALVE.
3. Bypass the LOW PRESSURE SWITCH.
4. Run the compressor until a vacuum is achieved.
5. Close the DISCHARGE SERVICE VALVE on the compressor.

6.Vent high to low through the manifold set. I.E. cap off the yellow line and open both blue and red wheels. pressure should now be low on both sides (2 to 5 psi maybe). change switches and open valves. run and set switches.
7. pub.

Re: Compressor Pump Down

Originally Posted by frank

How can you have the high and low pressure tappings connected to the compressor head?

On most semi-hermetic comps there is an access plug to both HP and LP side of the head. they take there pressure from the low side and high side of the cylinder head. You can just about see the two plugs on this comp

Re: Compressor Pump Down

Originally Posted by slingblade

6.Vent high to low through the manifold set. I.E. cap off the yellow line and open both blue and red wheels. pressure should now be low on both sides (2 to 5 psi maybe). change switches and open valves. run and set switches.

sling.

slingblade,

I really like your quick-and-easy proceedure; however, what's the purpose of venting high to low? All I care about is getting the gas out of the compressor head before I remove the switch probes. Correct?

Then, after the new probes are installed, I can purge out the air through my gauge set by cracking open the SUCTION SERVICE VALVE. Correct?

Re: Compressor Pump Down

g day kettler
i dont want to be rude or offend but this is basic friggie stuff mate....how service valves work an whats in comp is first year stuff...i am concerned for your safety and the safety of others...if you dont have a clear understanding of the equipment you are working with get someone who does to help you and teach you...sorry if this sounds a bit hard but you can get hurt if you do it wrong

Re: Compressor Pump Down

Originally Posted by MRC Guts

g day kettler
i dont want to be rude or offend but this is basic friggie stuff mate....how service valves work an whats in comp is first year stuff...i am concerned for your safety and the safety of others...if you dont have a clear understanding of the equipment you are working with get someone who does to help you and teach you...sorry if this sounds a bit hard but you can get hurt if you do it wrong

For all the forum members sanity and thoughts stop giving Kettler advice he's going to kill himself or the poor person next to him. Next he'll be asking which way the wires go on?

Re: Compressor Pump Down

Originally Posted by KETTLER

Thanks MRC Guts. I'm educated, experienced, and certified in refrigeration; however, I don't know EVERYTHING. I like to thoroughly think things through before I start turning wrenches. I think you can see from this string that there are many ways to 'skin a cat'. KETTLER

Re: Compressor Pump Down

I have been following this thread with interest. I choose not to respond to this initially because of the nature of the basic question. One of the members mentioned this is "first year stuff" and he is exactly right.

If a person has been working on refrigeration systems for some time and does not know how to pump down a compressor, something is wrong with this picture.

Originally Posted by KETTLER

I think you can see from this string that there are many ways to 'skin a cat'.

Never, ever assume this. Just because you get multiple opinions on how to do something does not mean they are all correct. That's a dangerous way to service systems I'm afraid.

Re: Compressor Pump Down

Cheers to ya all,

Iceman n LRAC are definitely right.
We don't need schools, university and educator now do we.
This guy says he has had knowledge and experience and oh my god, ''CERTIFICATE''
And yet he can't perform pump down, maybe, he may be able to conduct liquid transfer.
As sherlock says, ''Elementary my dear Watson''.

Re: Compressor Pump Down

hi there!
Option 1. recover all the refrigerant if you are familiar with the process.

If there is a shut-oof valve on both inlet and outlet of receiver then apply this procedure
Option 2. Pumpdown the refigerant. meaning
1.-connect your gauges to the compressor valves while both on back seat.

2.-Front seat(close) the valve after the liquid receiver.
3.-adjust cut-out pressure on LP switch to cut at
pressure below vacuum.
4. connect your gauge manifold to the compressor valves (HP and LP). Use a vacuum pump to remove air from the gauge lines with the compressor valves front- seated(close).
5.Then open the valves to almost intermediate position which will allow reading to be registerred on the gauge scale and also allow you to quickly close them later.
6. Run the unit and pumpdown will begin if the compressor cut-out too early on the LP swith , then readjust the cut-out pressure to cut out at a pressure under vacuum. Close (Frontseat) inlet of receiver.You will not be able to recover the left over a 100%. Then the decision is left with you
7.When the compressor cuts-out on a pressure below vacuum, then quickly front-seat both compressor valves

Re: Compressor Pump Down

Make sure the Lp and Hp parts of your dual Lp/Hp switch are the same way round if you are replacing it with a different make of switch. Ive seen danfoss ones replaced with ranco and on one the lp is on the lefthand side and on the other it was on the rigthhand side, so when changed it had the Lp hose going to the Hp switch and vice versa.
And any connections you disturb really need pressure testing with OFN to be sure you have no leaks and the evacuating.

Cheers Jon

Last edited by monkey spanners; 19-02-2007 at 07:15 PM.
Reason: dog stood on keys and posted before finished

Re: Compressor Pump Down

You must be one of the most fortunate forum members who has scrapped through on the information supplied to carry out out a simple pumpdown on a compressor. Do yourself a favour and get some proper training in this trade, if you have a certificate it must have been done on your computer.

from the first post on the 14/02/07 its took you 16 days to carry out the procedure, you must also be fortunate to have the most understanding customer in the WORLD.

g day kettler
i dont want to be rude or offend but this is basic friggie stuff mate....how service valves work an whats in comp is first year stuff...i am concerned for your safety and the safety of others...if you dont have a clear understanding of the equipment you are working with get someone who does to help you and teach you...sorry if this sounds a bit hard but you can get hurt if you do it wrong

where people take care about you I do not think this can come from some amateurs but you do

Please think again, about all, and admit your mistakes (at least to yourself) and you'll see we are not so bad guys.

Hope you will not misinterpret all of this

Best regards, Josip

It's impossible to make anything foolproof because fools are so ingenious... Don't ever underestimate the power of stupid people when they are in large groups.

Please, don't teach me how to be stupid....No job is as important as to jeopardize the safety of you or those that you work with.

Re: Compressor Pump Down

Originally Posted by taz24

I would just shut the suction valve while the comp is running. Then when the comp shuts down shut the discharge valve. The amount of gas in the comp will be minimal. To get the pressure even lower short out the lp switch and let the comp run into a vac. When all valves are closed vent the discharge gas from the comp head back to the suction and that will reduce further any gas loses.
Change the switches and then test like normal.

Same way I do it Taz. The remaining gas will be indeed very small, just the portion above the piston and the very small volume in the discharge valve.
This is something you don't find in schoolbooks but only can learn in practice, which you have.

Last edited by Peter_1; 17-04-2007 at 07:32 AM.

It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

Re: Compressor Pump Down

[quote=Peter_1;61238]

Originally Posted by taz24

Same way I do it Taz. The remaining gas will be indeed very small, just the portion above the piston and the very small volume in the discharge valve.
This is something you don't find in schoolbooks but only can learn in practice, which you have.

Thankyou Peter.

Iv'e been at it for 28 years now.
I'm still learning.
I was taught by some good engineers and was taught to leave the system running if possible no mater what the fault.

Re: Compressor Pump Down

dont know how to change a pressure control?? the system pumps down every cycle. and i dont know to many people who pump down the system to change a switch. if you do vent refrigerant not "***** sorry pet peeve" dont advertise the fact

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